The present invention relates to a pneumatic tire, more particularly to an arrangement of strain sensors fixed to a tire sidewall portion capable of improving the precision of determining tire force.
In recent years, in order to assure the safety, stability and the like of the vehicles, various computer-aided control systems for the vehicles, e.g. ABS (Anti Lock Brake System), TCS (Traction control system), VSC (vehicle stability control system) and the like have been developed and in practical use.
In such vehicle control systems, it is very important to correctly know various conditions of the rolling tires in real time under ever-changing driving situation. For that purpose, it is especially useful to know a longitudinal force, a lateral force and a vertical force, namely, three translational forces in the back-and-forth direction, right-and-left direction and up-and-down direction, applied to the ground contacting patch of the tire during running.
In the U.S. Pat. No. 7,249,498, we proposed a technique for determining the above-mentioned tire forces of a rolling tire by utilizing the deformation of the tire itself, wherein the strain of the tire is measured at circumferentially different fixed measuring positions, using strain sensors fixed to a sidewall portion of the tire, and the tire force is calculated, using the obtained data on the strain. Usually, a strain sensor has a directivity due to the geometrical structure thereof, and it has the most sensitive direction N to the strain. Therefore, in the above-mentioned technique, all of the sensors are oriented toward the same directions. The term “same directions” means that, as shown in FIG. 12, in a tire sidewall portion (b), the directions N of the sensors (a) are inclined towards one circumferential direction at the same angle θ (inclusive of 0 degree) with respect to the respective radial directions (r) at the positions of the sensors.
In the process of improving the accuracy of the calculated tire force, it was found that in particular combinations of the measuring position, the orientation angle, the radial position of the sensors and the type of the sensors, with respect to a tire force, correlation between outputs of the sensors becomes very strong, and as a result, it becomes difficult to decompose the force applied to the tire into the required force components, and the degree of accuracy is decreased.